1. Field of Invention
The present invention relates to a solenoid valve for a liquid propane injection system, and more particularly, to a solenoid valve for a liquid propane injection system that prevents bubbles from flowing into a fuel pump when a vehicle traveling at low speed is instantaneously and rapidly accelerated.
2. Description of Related Art
In general, as shown in FIG. 1, an LPI (Liquid Propane Injection) system is a system in which a fuel pump 2 pumps up liquid fuel stored in a bomb 1, the pumped fuel is injected into the combustion chambers of cylinders by injectors 3 through a pressure regulator, and the remaining fuel that fails to be injected into the combustion chamber by injectors 3 returns to bomb 1 through a return valve, and the system can improve the output and reduce the exhaust gas.
The fuel pump of the LPI system is usually disposed in the bomb and in this case it is not easy to maintain and repair the fuel pump, such that fuel pump 2 may be disposed outside bomb 1, as shown in FIG. 1.
In the LPI system with fuel pump 2 outside bomb 1, the fuel in bomb 1 flows through a solenoid valve 10 and then is supplied to fuel pump 2.
Solenoid valve 10, as shown in FIGS. 2 and 3, has a plunger housing 12 at one side from a tool-coupling portion 11 and a bomb-coupling portion 13 at the other side. A plunger 14 is inserted in plunger housing 12 and a pressure valve 15 is disposed in bomb-coupling portion 13, in which one end of pressure valve 15 is connected with plunger 14 and the other end is exposed to the outside through bomb-coupling portion 13.
In this structure, a thread is formed on the outer circumferential surface of bomb-coupling portion 13, such that bomb-coupling portion 13 is thread-fastened to a bomb housing 1a. 
When bomb-coupling portion 13 is thread-fastened to bomb housing la, pressure valve 15 protruding through bomb-coupling portion 13 is positioned between a fuel intake port 21 and a fuel discharge port 22.
Further, in solenoid valve 10, an armature 16 is connected to plunger housing 12 and a spring 17 elastically supporting plunger 14 is disposed between plunger 14 and armature 16, such that armature 16 fixes a solenoid coil 18 wound on plunger housing 12.
Further, an O-ring 23 keeping bomb housing la hermetic is disposed between tool-coupling portion 11 and bomb-coupling portion 13 and an O-ring 24 keeping fuel discharge port 22 hermetic is disposed on the outer circumferential surface of the end of pressure valve 15.
Solenoid valve 10 having the configuration described above keeps open such that fuel supply port 21 and fuel discharge port 22 are connected, by receiving power from a battery when the engine starts.
However, bubbles 25 are produced by evaporation of the fuel in solenoid valve 10 that is operated by the power from the battery because the temperature of solenoid coil 18 that generates heat is higher than the temperature of the fuel, and bubbles 25 produced as described above remain in the gap between plunger housing 12 and plunger 14, as shown in FIG. 3.
Since the flow speed of the fuel is low when a vehicle travels at low speed, bubbles 25 keep remaining in the gap between plunger housing 12 and plunger 14 and do not flow into fuel pump 2, while the flow speed of the fuel rapidly increases when the vehicle that has traveled for a predetermined time at low speed is instantaneously accelerated, such that bubbles 25 flow into fuel pump 2 through fuel discharge port 22, as shown in FIG. 4.
As bubbles 25 flow into fuel pump 2, as described above, fuel pump 2 loses the function of instantaneously sending the fuel and fuel is not smoothly supplied to injectors 3, such that the traveling of the vehicle becomes unstable.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.